headline that rocked the city of Houston tonight the pretty middle schoolteacher and the boy. What followed would be any parent's niekt Mary. New developments. Late today, she received her punishment. Reporter: It is the story thrust back into the spotlight just this week. After the first headlines shocked much of Houston, a parent's nightmare come true. He's a child. Reporter: A married middle school teacher they had trusted with their son was having sex with him. And tonight, for the first time, the secret that began in room 308 is finally unraveling. Alex and jenny pallais will never forget that first day at memorial middle school, one of the top schools in Houston. Bringing their son to that front door, newly adopted, rescued from distant relatives from a life of poverty in Costa Rica. They began the adoption process when he was just 9 years old. It took five years to get him here. Do you remember the trip to go get him, to bring him to America? Oh, definitely, and he was so excited. Like, "Oh, my god, this is my new life." Reporter: His new life in America. When we arrived to Houston, he was so surprised, amazed at the buildings, how tall the buildings were. He was so happy to be at his new home. Reporter: And soon, his new school. I walked jimmy to school. He was very nervous. Reporter: Do you remember your first day of school? I didn't like it. Reporter: You walked into that school not speaking a word of English. No. I knew just hello and that's it. Reporter: You said to jimmy, "You will survive this." Oh, yes. Reporter: It will get better. It will get better. It will get better. Reporter: This boy came to playing soccer, of college one day. One of his first trips, to nasa, with his new parents. This is the young face of the boy who was also getting help at school. There was an English teacher assigned to give him that extra help with his classes. 28-year-old Kathryn Camille Murray, who was married. Some of the boys thought Ms. Murray was pretty. Do you remember the first time you met her? Yes. Reporter: Was she nice? Yes, she was nice. She started helping me with my home work. Reporter: He found comfort in her classroom. You would take all your other classes and then you would go to her at the end of the day for help or sometime during the day for class? The teacher and student were growing closer. When do you start hearing about miss Murray? We went to the open house and I say, "Hello, miss Murray, I'm jimmy's mom." And immediately she looks at me and says, "Oh, jimmy's my favorite student. He's so well behaved." Sflr really? That that struck you as strange? I thought it was kind of strange. Reporter: And what was jimmy saying about miss Murray at home? Oh, she's so pretty. And I say, yeah, she's a pretty lady. Hey, every kid goes through that, has a crush on a teacher. Reporter: So, you're thinking this is our adolescent son. This is an adolescent. Reporter: "With a crush." Son with just a simple crush, that's it. We thought nothing of it. Reporter: And in all of his classes, jimmy is getting As and Bs. It was like, okay, so she's actually doing good for him. Helping him. Reporter: But there was more. At school jimmy says there was something about the way she would look at him. When you would walk into that room, would she smile? She looked at me different. Reporter: She looked at you differently? Yes. Reporter: Is that when you sensed that she had feelings for you, too? Uh-huh, yes. Reporter: Before Christmas break, he writes a note revealing his love for his teacher. But then tears it up into pieces and gave it to her to throw away. Instead, she keeps the letter. And when he returns to school, a surprise. She said, "I read your letter." Reporter: She put it back together. Yes, and she told me, "I really like you, for real." And she told me, "I know, but we can't have anything." Reporter: She told you, you couldn't have anything? Jimmy is staying after school nearly every day now. Then one afternoon he doesn't come home from school. His parents frantically begin looking for him through the empty hallways, everywhere. Even room 308, his father finds the custodian. We saw the custodial lady. And she said, oh yes, they were just here. They left. Reporter: There was no sign of him. Suddenly jimmy appears at home. Holding his arm like this. With blood, yes. He couldn't. He had no words. And as soon as he spoke, he just started crying. Reporter: He would cry for nearly an hour, and then offer a story. Jimmy told his parents he'd been in the car with Ms. Murray and they had an argument. He told us he was in the car and jumped out of the car. So he's like, "What happened?" And the only thing he said was, "I told her that I like her." And my wife and I are looking at each other, "Okay, this sounds like a lover's quarrel." Reporter: They immediately reach out to Ms. Murray. But she mentions nothing about jimmy being in her car. So at that moment, you think there's something going on. She is lying. Reporter: They tell Ms. Murray their son needs to be taken out of her class. Weeks go by. Life at home returns to Normal. Every night. Every night. Reporter: You all sit down at dinner table? We're at the dinner table. Reporter: And he'd stop talking about Ms. Murray. He'd stopped talking about Ms. Murray. We thought it was over. Reporter: But it was far from over. They were now talking on Facebook. Jimmy says he messaged Ms. Murray that he wanted to kiss her. And that she replied, "I want to see that." She wanted you to kiss her? Yes. Monday I came to my school early and I went straight to her and I kiss her. When I stopped kissing her I walk to my first class. Reporter: You were thinking to yourself you had to get back to her. Yes. Reporter: So you went back to her and you asked her how she felt about what happened. Yes, and she told me, "Okay, I want you to kiss me again." So that's when I kiss her again. Reporter: That's when it started. Yes. Reporter: Physically. Did she ever say to you, "This is wrong?" After I kiss her. Reporter: And tonight revealed for the first time here on "20/20" school surveillance tapes showing the teacher meeting privately in her classroom. Behind closed doors, again and again, with the middle school student. She can be seen scanning the hallway, sometimes walking out with jimmy. Other days they leave in different directions. While at home, what jimmy's parents think is a welcome sign, the school dance. And jimmy wants to go with the friends he's now made. No sign of Ms. Murray. And are you hoping that jimmy's going to find a girl his own age to have a crush on? Of course. Of course. Reporter: But the girl waiting at the dance, Ms. Murray, across the street from the school. In the church parking lot. His dad had no idea. I dropped him off and he saw me leaving. And then he moved on alert to meet her across the street. Reporter: And she's waiting, in of all places, the church across the street. Yes. Reporter: So, you would talked to miss Murray during the day. You said, "My dad's gonna bring me to the dance." And the two of you had a plan. Yes. Reporter: The boy she'd been warned to stay clear of, she was now taking away from that school dance. She had her own playlist. Tonight, "20/20" obtaining the video, the images the night she checked into a nearby hotel. Then her teenaged student through that side door. Did anything happen? Yes. We have sexual relations. Reporter: You had sex with her? Yes. Reporter: A secret the teacher helped Jimmie keep. But not for long. Suddenly, a disturbing phone call from the principal. He confided in another teacher that he had kissed miss Murray. Reporter: That "I kissed miss Murray." Yes. That's correct. Reporter: They took selfies. Pictures of themselves kissing. And tonight, for the first time here, we see them. They would become a key part of this case. Then another major blow. Jimmy and his mother sitting together, when suddenly her phone goes off. She'd let jimmy borrow it. The teacher, miss Murray, thought she was texting jimmy. But, the mother was receiving the texts. It read in part -- "You know I love you. I don't know what we're going to do, but we're going to be happy together. I miss you." Now a mother looking down at her cell phone, stunned. I said, "Jimmy, I need to go to the restroom, I have to put water on my face." And I say, "Okay, this is not happening." Reporter: And that mother had not even heard the worst of it.

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